The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure.
Engines combust a mixture of air and fuel to produce drive torque and propel a vehicle. More specifically, air is drawn into an engine through a throttle valve. Fuel provided by one or more fuel injectors mixes with the air to form the air/fuel mixture. The air/fuel mixture is combusted within one or more cylinders of the engine to produce torque. An engine control module (ECM) controls torque output by the engine.
Exhaust gas resulting from combustion of the air/fuel mixture is expelled from the engine to an exhaust system. One or more oxygen sensors measure oxygen in the exhaust gas and output signals accordingly. The ECM selectively adjusts the air and/or fuel of the air/fuel mixture based on the output of the oxygen sensors. For example, the ECM may adjust the air/fuel mixture to produce a stoichiometric air/fuel mixture (e.g., 14.7:1).
Adjustments of the air/fuel mixture also vary the components of the resulting exhaust gas. For example, combustion of a lean air/fuel mixture (e.g., greater than 14.7:1) produces exhaust gas that is hotter than exhaust gas produced when a stoichiometric air/fuel mixture is combusted. The exhaust gas resulting from combustion of the lean air/fuel mixture may also include a greater concentration of nitrogen oxides (NOx) than exhaust gas produced by combustion of the stoichiometric mixture. A rich air/fuel mixture (e.g., less than 14.7:1) may produce cooler exhaust gas having a greater concentration of carbon oxides than the exhaust gas produced by combustion of the stoichiometric mixture.